It is known that vehicle wheels are generally made up of a cylindrical metal rim having, at the axial ends, ring-shaped flanges between which is defined a channel for the interlock of an elastic tire, the side portions of which, the so-called “beads”, are positioned fast up to the ring-shaped flanges.
The need is also known to perform frequent balancing operations that consist in applying weights, made of lead or other material, at predetermined points of the wheel and along the rim.
The fitting of the weights offsets the presence of any tire and/or rim irregularities during the rotation of the wheel.
To perform such operations, balancing machines are commonly used that comprise a supporting structure for wheel gripping and rotation means, such as a horizontal shaft that can turn axially by means of motor means and onto which the wheel rim is keyed.
The measurement of the wheel unbalance is detected during rotation by suitable electronic or electromechanical devices, such as force transducers fitted along the horizontal shaft.
Other characteristic measurements are generally added to the unbalance measurement such as the measurement of the wheel roundness, the eccentricity of the wheel, the amount of tread wear, etc. Such measurements are normally performed by means of suitable measuring sensors, with or without contacting the wheel (for example feeler pins or optical sensors).
Each of the detected measurements is normally related to a respective angular position of the wheel on the rotation axis detected by an angular position transducer (encoder) associated with the horizontal shaft.
In particular, the unbalance and the other specific measurements made on the wheel are performed by sampling the signals coming from the respective measuring sensors at preset and constant angular intervals determined by the technical characteristics of the encoder.
These known balancing machines are however susceptible to upgrading, in particular, in order to upgrade the quality and the precision of the measurements taken.
In fact, the frequency of samplings made by the measuring devices on the wheel is closely tied to predetermined angular positions and is restricted by the technical characteristics of the encoder. In particular, the angular resolution of the encoder, generally suitable for measuring unbalance, can be insufficient and not allow sufficiently accurate measurements in case, for example, of measuring the roundness or the eccentricity of the wheel. In fact, the low resolution of the measurements made, together with the presence of numerous branched grooves that extend irregularly on the surface of the tread, tends to falsify the testing of the tire characteristics.